Sway mitigation in an elevator system

ABSTRACT

An elevator system ( 20 ) includes an elongated member ( 30, 32, 34 ) that may sway under certain conditions. At least one mitigation member ( 80 ) is strategically positioned in a mitigation position corresponding to a location of an anti-node ( 48, 54, 56, 66, 68, 70 ) of the elongated member ( 30, 32, 34 ) for a given sway condition. In a disclosed example, a controller ( 38 ) deploys a mitigation member ( 80 ) at a mitigation position for a given sway condition determined by the controller ( 38 ). In one example, a plurality of sway mitigation members ( 80 ) are strategically positioned at various mitigation positions within a hoistway ( 26 ). In another example, a sway mitigation member ( 80 ) is selectively moveable within a hoistway ( 26 ) between a plurality of mitigation positions.

BACKGROUND

1. Field of the Invention

This invention generally relates to elevator systems. More particularly,this invention relates to minimizing sway of one or more verticalmembers in an elevator system.

2. Description of the Related Art

Many elevator systems include an elevator car and counterweight that aresuspended within a hoistway by roping comprising one or more loadbearing members. Typically, a plurality of ropes, cables or belts areused for supporting the weight of the elevator car and counterweight andfor moving the elevator car to desired positions within the hoistway.The load bearing members are typically routed about several sheavesaccording to a desired roping arrangement. It is desirable to maintainthe load bearing members in an expected orientation based upon theroping configuration.

There are other vertically extending members within many elevatorsystems. Tie down compensation typically relies upon a chain or ropingbeneath an elevator car and counterweight. Elevator systems typicallyalso include a traveling cable that provides power and signalcommunication between components associated with the elevator car and afixed location relative to the hoistway.

There are conditions where one or more of the vertically extendingmembers such as the load bearing member, tie down compensation member ortraveling cable may begin to sway within an elevator hoistway. This ismost prominent in high rise buildings where an amount of building swayis typically larger compared to shorter buildings and when the frequencyof the building sway is an integer multiple of the natural frequency ofa vertically extending member within the hoistway. There are knowndrawbacks associated with sway conditions.

Various proposals have been made for mitigating or minimizing sway of avertically extending member within a hoistway. One example approachincludes using a swing arm as a mechanical device for inhibiting sway ofa load bearing member, for example. U.S. Pat. No. 5,947,232 shows such adevice. Another device of this type is shown in U.S. Pat. No. 5,103,937.

Another approach has been to associate a follower car with an elevatorcar. The follower car is effectively suspended beneath the elevator carand is positioned at the midpoint between the elevator car and a bottomof a hoistway for sway mitigation purposes. A significant drawbackassociated with this approach is that it introduces additionalcomponents and expense into an elevator system. In addition to thefollower car and its associated components, the size of the elevator pitmust be larger than is otherwise required, which takes up additionalreal estate space or introduces additional costs or complexities indesigning and building the elevator shaft. Additionally, follower carshave only been considered to mitigate sway of compensation ropes andthey introduce additional potential complications into an elevatorsystem.

Another approach includes controlling the position of an elevator carand the speed with which the car moves within a hoistway for minimizingthe sway. It is known how to identify particular elevator car positionswithin a hoistway corresponding to particular building sway frequenciesthat will more effectively excite the vertically extending members. Oneapproach includes minimizing the amount of time an elevator car isallowed to remain at such a so-called critical position when conditionsconducive to sway are present.

While the previous approaches have proven useful, those skilled in theart are always striving to make improvements. This invention includes anadvanced technique that provides enhanced sway mitigation.

SUMMARY

An exemplary method of controlling sway of an elongated member in anelevator hoistway includes determining at least one location within thehoistway corresponding to an anti-node of the elongated member if atleast one condition conducive to sway exists. A sway mitigation memberis positioned at a mitigation position within a selected range of thedetermined location corresponding to the anti-node at least when thecondition conducive to sway exists.

One example includes permanently positioning the sway mitigation memberat the mitigation position. Another example includes moving the swaymitigation member from another position within the hoistway to themitigation position if the condition conducive to sway exists.

In one example, the sway mitigation member is supported for movementalong a stationary surface within the hoistway. In another example, thesway mitigation member is supported on an elevator car or acounterweight that is moved within the hoistway to appropriatelyposition the sway mitigation member.

An exemplary elevator system includes at least one elongated memberwithin an elevator hoistway. The elongated member has at least oneanti-node at a determined location within the hoistway if at least onecondition exists that is conducive to sway of the elongated member. Atleast one sway mitigation member is positioned at a mitigation positionwithin a selected range of the location corresponding to the anti-nodeat least when the condition conducive to sway exists.

In one example, the sway mitigation member remains at an essentiallyfixed position within a hoistway. In another example, the swaymitigation member is selectively moveable within the hoistway to adesired mitigation position corresponding to a current condition.

Strategically positioning a sway mitigation member at a position withina hoistway corresponding to a location of an anti-node of an elongatedmember within the hoistway facilitates enhanced sway mitigation. In oneexample, a technique of controlling the position, speed or both of theelevator car is combined with the strategic positioning of the swaymitigation member.

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrated selected portions of an elevator systemthat may incorporate an example embodiment of this invention.

FIG. 2 schematically illustrates sway behavior of an elongated memberwithin an elevator hoistway.

FIG. 3 schematically illustrates one example approach of sway mitigationdesigned according to an example embodiment of this invention.

FIG. 4 schematically illustrates another example approach.

FIG. 5 schematically illustrates another example approach.

DETAILED DESCRIPTION

Example embodiments of this invention provide sway mitigation within anelevator hoistway to control the amount of sway of one or more elongatedmembers such as a load bearing member (e.g., an elevator rope or belt),a tie down compensation member or a traveling cable, for example.Strategically positioning a sway mitigation member at a position withina hoistway corresponding to an anti-node of the elongated member for agiven potential sway condition provides enhanced sway mitigationcompared to previous approaches.

FIG. 1 schematically shows selected portions of an elevator system 20.An elevator car 22 and counterweight 24 are moveable within a hoistway26 in a known manner. The elevator car 22 and counterweight 24 aresupported by a load bearing assembly including roping or belts thatsupport the weight of the elevator car 22 and counterweight 24 andprovide for moving them in a known manner. An example load bearingmember 30 is shown in FIG. 1. In the illustrated example, a tie downcompensation member 32 is associated with the elevator car 22 and thecounterweight 24 to provide tie down compensation in a known manner. Atraveling cable 34 provides for communicating electrical power andsignals between components associated with the elevator car 22 and atleast one other device typically located in a fixed position relative tothe hoistway 26.

Each of the load bearing member 30, tie down compensation member 32 andtraveling cable 34 is an elongated vertical member within the hoistway26. Any one or more of the elongated vertical members 30, 32, 34 maybegin to sway within the hoistway 26 if appropriate conditions conduciveto sway exist. Building sway is known to induce sway of an elongatedvertical member within a hoistway especially when the frequency of thebuilding sway is an integer multiple of a natural frequency of theelongated member.

The example of FIG. 1 includes a sensor 36 that operates in a knownmanner to provide an indication of any existing building sway. In oneexample, the sensor 36 is a pendulum-type sensor. Another exampleincludes a wind anemometer. A controller 38 communicates with the sensor36 and determines whether a condition exists that is conducive to swayof at least one of the elongated vertical members within the hoistway26. The controller 38 is programmed to respond to such a condition bycontrolling the operation of at least one sway mitigation member as willbe described below. In one example, the controller 38 is alsoresponsible for controlling the position, speed or both of the elevatorcar 22 in an manner that is intended to minimize an amount of sway. Inone example, the controller 38 uses known elevator car position andspeed control techniques for this purpose. The controller 38 in oneexample also uses information regarding a load on the elevator car 22.

FIG. 2 includes a graphical plot 40 that schematically illustrates swaybehavior of an example elongated member within a hoistway. For purposesof discussion, the load bearing member 30 will be considered as anexample elongated member for the remainder of this description. FIG. 2includes a static desired orientation of the load bearing member 30shown in phantom as a vertical line. This orientation corresponds to adesired orientation of the load bearing member 30 based upon a selectedroping arrangement, for example.

In FIG. 2, L represents a length of an example load bearing member 30and x represents a distance along the vertical axis. Y is a lateraldistance along the horizontal axis and y0 is the maximal sway in adirection along the horizontal axis.

Several conditions may exist that will be conducive to the load bearingmember 30 swaying within the hoistway 26. One sway condition is shown at42. When the frequency of building movement or sway corresponds to thenatural frequency of the load bearing member 30 (given a currentposition of the elevator car, for example) an N=1 mode of sway asschematically shown at 42 may exist. In this condition, the load bearingmember 30 has a node at 44 and at 46, which correspond in one example tothe connection between the load bearing member and the elevator car andan interface between the load bearing member and a traction sheave nearopposite ends of the portion of the load bearing member 30 shown in FIG.2. Between the two nodes 44 and 46 is an anti-node at a location 48(x*/L). The anti-node corresponds to the largest displacement of theload bearing member 30 from the desired position shown in phantom inFIG. 2. The anti-node 48 is at a location corresponding to a greatestamplitude of movement in a horizontal or lateral direction of the loadbearing member 30 in the N=1 mode of sway.

The example conditions schematically represented in FIG. 2 are for aparticular case and depend on the elongated member tension, mass perunit length, and member length. For example, the distance x*corresponding to a node location along the length L represents one loadcondition. Other load conditions may result in values of x*/L that aredifferent than those in the Figure. In one example, the controller 38uses information regarding a current load on the elevator car 22 forpurposes of determining the location of the anti-node(s) for a givenmode of sway.

An example embodiment includes strategically positioning a swaymitigation member at a mitigation position within a selected range of alocation of an anti-node of an elongated vertical member such as theload bearing member 30. In some examples, the sway mitigation memberwill be located at a mitigation position corresponding as closely aspossible to the expected anti-node location for a given condition. Inanother example, an acceptable range of mitigation positions includingthe location of the anti-node may be used. In the case of an N=1 mode ofsway, there may be considerable latitude in the desired position of thesway mitigation member, for example. Provided that the sway mitigationmember is strategically positioned close enough to the location of theanti-node, the benefit of the example approach can be achieved.

As can be appreciated from the illustration, the location of theanti-node 48 is not at the midpoint of the length of the load bearingmember 30 shown in FIG. 2. This is because the tension on the loadbearing member 30 is not constant along its length but decreases inmagnitude from top to bottom because of the per unit length weight ofthe load bearing member 30. One shortcoming of previous attempts at swaymitigation has been to position a sway mitigation member at the midpointof the vertical length of a load bearing member. The thinking behindthat approach was to effectively reduce the effective length of the loadbearing member in half to change the effective natural frequency. Undervarious conditions, such a position of a sway mitigation member will notprovide the desired effect.

Another sway condition is shown at 50. In this condition, the loadbearing member 30 has nodes at 44, 46 and 52. The nodes correspond topositions of the load bearing member 30 that are coincident with thedesired orientation shown in phantom. In this N=2 mode, the buildingfrequency of movement is twice that of the natural frequency of the loadbearing member 30. Anti-nodes exist at 54 and 56 in this condition. Ascan be appreciated from the illustration, the node 52 is not at the midpoint of the length of the load bearing member 30 and the anti-nodes 54and 56 are not symmetrically positioned relative to the node 52 nor themid-point along the length of the load bearing member 30. Again, thistype of configuration is due to the tension on the load bearing member30 and the weight of the load bearing member 30 itself under theillustrated conditions.

A third sway condition is shown at 60. In one example this is an N=3mode where the building movement frequency is three times the naturalfrequency of the load bearing member 30. In this condition, the loadbearing member 30 has nodes at 44, 46, 62 and 64. Anti-nodes are at 66,68 and 70.

Determining the locations of the anti-nodes in one example includessolving an equation that is, or a system of equations that are,indicative of the response of an elongated vertical member in a hoistwayto building sway displacements. One example uses known behaviors ofsuspended vertical members and incorporates information corresponding tohow elevator system components can be fitted to such a model. Given thisdescription, those skilled in the art will realize how best to determinethe locations of the anti-nodes for a given elongated vertical member ina particular elevator system for any number of order modes for anyelevator car vertical location.

Positioning a sway mitigation member in a mitigation position in oneexample includes positioning the sway mitigation member within aselected range of an anti-node location. The acceptable range in oneexample varies depending on the current sway condition. Referring toFIG. 2, for example, when a sway mitigation member is positioned in amitigation position corresponding to the location of the anti-node 48, awider range will be useful compared to a range that will be useful for amitigation position corresponding to the location of the anti-node 68.As can be appreciated from the illustration, a particular distance fromthe exact location of the anti-node 48 may still position the mitigationmember in a manner that is effective for controlling sway of the loadbearing member 30. That same distance from the location of the anti-node68 may effectively position the sway mitigation member at a locationcorresponding to the node 62, which would be ineffective under somecircumstances for maximum possible sway control. Given this description,those skilled in the art will realize how to set desired limits on anacceptable range of distance between a mitigation position and ananti-node location to meet the needs of their particular situation.

In the example of FIG. 2, it may be possible to position a mitigationmember at a single mitigation position that is effective for addressingthe anti-node locations corresponding to the anti-nodes 56 and 68. Ifthe distance between the anti-nodes 56 and 68 is small enough and themitigation member is appropriately sized, a single mitigation positionmay be effective for addressing the anti-node 56 under one condition orthe anti-node 68 under a different sway condition.

Strategically positioning a sway mitigation member at a mitigationposition corresponding to a location of an anti-node provides enhancedsway mitigation compared to previous approaches. By minimizing theamount of movement of an elongated vertical member at the position wherethe greatest amount of such movements would otherwise occur hasbenefits. There are several example approaches to strategicallypositioning a sway mitigation member in this manner that are consistentwith an embodiment of this invention.

FIG. 3 schematically illustrates one example approach. In this example,at least one sway mitigation member 80 is supported in a fixed positionwithin the hoistway 26 so that when the sway mitigation member 80 isdeployed, it is in a mitigation position corresponding to the locationof an expected anti-node of the load bearing member 30. In one example,a sway mitigation member consistent with the teachings of U.S. Pat. No.5,947,232 is supported within the hoistway 26 such that it can bedeployed for purposes of sway mitigation. The sway mitigation member 80may be a swing arm, snubber or other mechanical device that limitslateral motion, for example.

The example of FIG. 3 includes a plurality of sway mitigation members atvarious locations within the hoistway 26. The sway mitigation member 80Amay be, for example, positioned at a position within the hoistway 26corresponding to the location of the anti-node 70 shown in FIG. 2. Thesway mitigation member 80B may be positioned in a mitigation positioncorresponding to the location of the anti-node 48. The sway mitigationmember 80C may be positioned in a mitigation position corresponding tothe anti-node 56.

In one example, the controller 38 determines what type of sway-conducivecondition exists. The controller 38 is programmed to use suchinformation and information regarding predetermined locations of one ormore anti-nodes of the load bearing member 30 under such a condition fordetermining which of the sway mitigation members in the example of FIG.3 to deploy. In other words, the controller 38 utilizes information fromthe sensor 36 and predetermined information regarding the expectedlocations of the anti-nodes for a given sway condition for purposes ofdetermining the locations at which a sway mitigation member should bedeployed. The location information in one example is specific for eachof a plurality of different load conditions. In some examples, only onesway mitigation member will be deployed at any given time. In otherexamples, multiple sway mitigation members may be used simultaneously atone sway mitigation position or multiple sway mitigation positions,depending on the particular condition.

In one example, in addition to deploying one or more sway mitigationmembers, the controller 38 controls the position, speed or both of theelevator car 22 to further minimize potential sway. In one example,whenever the determined building sway frequency is within about 10% ofthe natural frequency of the load bearing member 30, for particularlocations of the elevator car 22 within the hoistway 26, these locationsare considered so-called critical zones. In one example, the controller38 minimizes the amount of time the elevator car 22 remains in acritical zone and reduces a speed at which the elevator car 22 moveswithin the hoistway 26 compared to a normal, contract speed. Forexample, the elevator car 22 will not be allowed to remain parked at alanding corresponding to a critical zone for more than a preset time ifa condition conductive to sway exists. Instead, the elevator car 22moves to another location

In one example, the controller 38 includes a database such as a look uptable that has information corresponding to various conditions conduciveto sway, corresponding critical zone locations of an elevator car,locations of anti-nodes and corresponding desired mitigation positionsof a mitigation member. The controller 38 uses this information fordetermining how best to implement speed and position control of theelevator car and at least one sway mitigation member to minimize orcompletely inhibit sway. In one example, the controller 38 includes suchinformation for each of a load bearing member 30, a tie downcompensation member 32 and a traveling cable 34.

FIG. 4 schematically illustrates another example approach. In thisexample, the sway mitigation member 80 is supported for verticalmovement along a vertical surface such as one of the walls in thehoistway 26. The sway mitigation member 80 in this example is controlledby the controller 38 to move as schematically shown at 82 among aplurality of mitigation positions, each of which may correspond to oneor more anti-node locations within the hoistway 26.

FIG. 5 schematically illustrates another example approach. This exampleincludes multiple elevator cars and counterweights within a hoistway 26.In this example, an elevator car 22B includes sway mitigation members80D that are useful for minimizing sway of the load bearing member 30that supports the elevator car 22A. The controller 38 in such an examplestrategically controls the position of the elevator car 22B to positionthe sway mitigation members 80D in a mitigation position for a givencondition.

The example of FIG. 5 also includes sway mitigation members 80Eassociated with the counterweight 24A. In such an example, the swaymitigation members 80E are useful for minimizing sway of the loadbearing member 30 supporting the counterweight 24B.

In the case of two cars 22A, 22B, if one of the cars 22A were parked ata lower lobby such that the vertically extending members thereof weresuspended in a critical zone, the other car 22B could be controlled soas to serve in a sway mitigation capacity at an anti-node of the car22A. Similarly, if one of the cars 22B were parked at an upper lobbysuch that its load bearing members were suspended in a critical zone,the other car 22A could be controlled so as to serve in a swaymitigation capacity at an anti-node of the car 22B.

Although not illustrated in FIG. 5, additional sway mitigation membersmay be associated with either of the elevator cars 22A, 22B or thecounterweights 24A, 24B for purposes of controlling sway of tie downcompensation members traveling cables or other elongated verticalmembers within the elevator system of the example of FIG. 5.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this invention. The scope of legal protection given tothis invention can only be determined by studying the following claims.

1. A method of controlling sway of an elongated member in an elevatorhoistway, comprising the steps of: determining at least one locationwithin the hoistway corresponding to an anti-node of the elongatedmember when at least one condition conducive to sway exists; andpositioning a sway mitigation member at a mitigation position within aselected range of the determined location at least when the at least onecondition exists.
 2. The method of claim 1, comprising permanentlypositioning the sway mitigation member at the mitigation position; andselectively deploying the sway mitigation member for controlling sway ofthe elongated member.
 3. The method of claim 1, comprising moving thesway mitigation member from another position within the hoistway to themitigation position if the at least one condition exists.
 4. The methodof claim 3, comprising supporting the sway mitigation member formovement along a stationary surface within the hoistway.
 5. The methodof claim 3, comprising supporting the sway mitigation member on at leastone of an elevator car or a counterweight; and moving the at least oneof the elevator car or the counterweight to a position that places thesway mitigation member in the mitigation position if the at least onecondition exists.
 6. The method of claim 1, comprising determining aplurality of locations each corresponding to an anti-node of theelongated member if one of a corresponding plurality of conditionsconducive to sway exists; and deploying the sway mitigation member at aselected mitigation position within a selected range of one of thedetermined locations if a corresponding one of the conditions exists. 7.The method of claim 6, comprising determining which of the conditionsexists; and moving the sway mitigation member to the correspondingmitigation position.
 8. The method of claim 6, comprising positioning asway mitigation member at a mitigation position corresponding to each ofthe determined plurality of locations; and selecting a corresponding oneof the sway mitigation members for the deploying if one of the pluralityof conditions exists.
 9. The method of claim 1, comprising determiningthe at least one location as a function of elevator car position in thehoistway; and controlling at least one of a desired elevator carposition or speed for minimizing an amount of possible sway if the atleast one condition exists.
 10. The method of claim 1, wherein theelongated member comprises at least one of an elevator load bearingmember; an elevator compensation member; or a traveling cable.
 11. Themethod of claim 1, comprising determining at least one critical zonewithin the hoistway corresponding to the at least one condition; andmoving an elevator car out of the at least one critical zone if the atleast one condition exists.
 12. The method of claim 1, comprisingreducing a speed of movement of an elevator car in the hoistway if theat least one condition exists.
 13. The method of claim 1, wherein theelongated member is associated with a first elevator car, the methodcomprising moving a second elevator car to the anti-node of theelongated member, when the at least one condition conducive to swayexists.
 14. An elevator system, comprising: at least one elongatedmember in a hoistway, the elongated member having an anti-node at apredetermined location if at least one condition exists that isconducive to sway of the elongated member; and a sway mitigation memberat a mitigation position in the hoistway within a selected range of thepredetermined location corresponding to the anti-node at least when thecondition conducive to sway exists.
 15. The system of claim 14, whereinthe sway mitigation member is permanently positioned near the mitigationposition.
 16. The system of claim 14, wherein the sway mitigation memberis selectively moveable from another position within the hoistway to themitigation position if the condition exists.
 17. The system of claim 16,wherein the sway mitigation member is moveable along a stationarysurface within the hoistway.
 18. The system of claim 16, comprising aplurality of elevator cars and associated counterweights within thehoistway; and wherein the sway mitigation member is supported formovement with at least one of the elevator cars or counterweights suchthat the corresponding elevator car or counterweight is moveable into aposition that places the sway mitigation member in the mitigationposition.
 19. The system of claim 14, comprising a plurality of swaymitigation members each at a mitigation position corresponding to adifferent location of an anti-node.
 20. The system of claim 19,comprising a controller that is configured to: (a) determine a currentcondition and a corresponding location of one of the anti-nodes; and (b)deploy a selected one of the mitigation members at a correspondingmitigation position.
 21. The system of claim 14, comprising a controllerthat is configured to: (a) determine the at least one locationcorresponding to the anti-node as a function of elevator car position inthe hoistway; and (b) control at least one of a desired elevator carposition or speed for minimizing an amount of possible sway.
 22. Thesystem of claim 21, wherein the controller is configured to move theelevator car out of a critical zone in the hoistway if the at least onecondition exists.
 23. The system of claim 21, wherein the controller isconfigured to reduce a speed of movement of the elevator car if the atleast one condition exists.
 24. The system of claim 14, wherein theelongated member comprises at least one of an elevator load bearingmember; an elevator compensation member; or a traveling cable.
 25. Thesystem of claim 14, comprising a sensor that is configured to provide anindication when the at least one condition exists.